<template>
  <scroll @scroll="scroll"
          :listen-scroll="listenScroll"
          :probe-type="probeType"
          :dataA="dataA"
          class="listview"
          ref="listview">
		<!-- 左侧歌手列表 -->
    <ul>
      <li v-for="(group,index) in dataA" :key="index" class="list-group" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <uL>
          <li @click="selectItem(item)" v-for="(item, index) in group.items"  :key="index" class="list-group-item">
            <img class="avatar" v-lazy="item.avatar">
            <span class="name">{{item.name}}</span>
          </li>
        </uL>
      </li>
    </ul>
		<!-- 右测字母列表 -->
    <div class="list-shortcut" @touchstart.stop.prevent="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove"
         @touchend.stop>
      <ul>
        <li v-for="(item, index) in shortcutList" :data-index="index"  :key="index" class="item"
            :class="{'current':currentIndex===index}">{{item}}
        </li>
      </ul>
    </div>
    <div class="list-fixed" ref="fixed" v-show="fixedTitle">
      <div class="fixed-title">{{fixedTitle}} </div>
    </div>
    <div v-show="!dataA.length" class="loading-container">
      <loading></loading>
    </div>
  </scroll>
</template>

<script>
  import Scroll from 'base/scroll/scroll'
  import Loading from 'base/loading/loading'
  import {getData} from 'common/js/dom'

  const TITLE_HEIGHT = 30
  const ANCHOR_HEIGHT = 18

  export default {
    props: {
      dataA: {
        type: Array,
        default:[]
      }
    },
    computed: {
      shortcutList() {//循环得到字母的首字母
        return this.dataA.map((group) => {
          return group.title.substr(0, 1)
        })
      },
      fixedTitle() { //字母列表的title头 边界问题
        if (this.scrollY > 0) {
          return ''
        }
        return this.dataA[this.currentIndex] ? this.dataA[this.currentIndex].title : ''
      }
    },
    data() {
      return {
        scrollY: -1, //监听时时滚动的位置
        currentIndex: 0,
        diff: -1
      }
    },
    created() {
      this.probeType = 3
      this.listenScroll = true
      this.touch = {}
      this.listHeight = []
    },
    methods: {
      selectItem(item) {
        this.$emit('select', item)
      },
      onShortcutTouchStart(e) {
				let anchorIndex = getData(e.target, 'index')
				// console.log( this.$refs.listviwe.scrollToElement( this.$refs.listviwe.listGroup[anchorIndex],0 ) ) //最初写法
        let firstTouch = e.touches[0] //获取第一个手指的位子
        this.touch.y1 = firstTouch.pageY
        this.touch.anchorIndex = anchorIndex//记录当前的点击的索引
        this._scrollTo(anchorIndex)
      },
      onShortcutTouchMove(e) {
        let firstTouch = e.touches[0]
        this.touch.y2 = firstTouch.pageY//相减可以得到滚动的高度 
        let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0
        let anchorIndex = parseInt(this.touch.anchorIndex) + delta//等到要滚动几个索引值
        this._scrollTo(anchorIndex)
      },
      refresh() {
        this.$refs.listview.refresh()
      },
      scroll(pos) {//从scroll派发出来的scroll的位置
        this.scrollY = pos.y
      },
      _calculateHeight() { //获取歌手列表的高度值
        this.listHeight = []
        const list = this.$refs.listGroup
        let height = 0
        this.listHeight.push(height)
        for (let i = 0; i < list.length; i++) {
          let item = list[i]
          height += item.clientHeight
          this.listHeight.push(height)	
        }
	      // (24)[0, 760, 1030, 1370, 1780, 1910, 2110, 2450, 2720, 3060, 3190, 3950, 4430, 4700, 4900, 5100, 5370, 5570, 5980, 6460, 7010, 7560, 7900, 9010
      },
      _scrollTo(index) { //封装了要滚动的条数位置
        if (!index && index !== 0) { //首尾2端点击无效
          return
        }
        if (index < 0) { //超出边界
          index = 0 
        } else if (index > this.listHeight.length - 2) {
          index = this.listHeight.length - 2
        }
				//点击字母表是滑动条位子不变 需要手动设置 watch
        this.scrollY = -this.listHeight[index]//手动设置滚动条位置
        this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)
      }
    },
    watch: {
      dataA() {
        setTimeout(() => {
          this._calculateHeight()
        }, 20)
      },
      scrollY(newY) { //比较数组的位置
        const listHeight = this.listHeight
        // 当滚动到顶部，newY>0
        if (newY > 0) {
          this.currentIndex = 0
          return
        }
        // 在中间部分滚动
        for (let i = 0; i < listHeight.length - 1; i++) {
          let height1 = listHeight[i]
          let height2 = listHeight[i + 1]
          if (-newY >= height1 && -newY < height2) {
            this.currentIndex = i
            this.diff = height2 + newY
            return
          }
        }
        // 当滚动到底部，且-newY大于最后一个元素的上限
        this.currentIndex = listHeight.length - 2
      },
      diff(newVal) {
        let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
        if (this.fixedTop === fixedTop) {
          return
        }
        this.fixedTop = fixedTop
        this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
      }
    },
    components: {
      Scroll,
      Loading
    }
  }

</script>


<style lang="less"  scoped>
   @import "../../common/stylus/variable.less";

   .listview{
     position: relative;
     width: 100%;
     height: 100%;
     overflow: hidden;
     background: @color-background;
     .list-group{
       padding-bottom: 30px;
       .list-group-title{
         height: 30px;
         line-height: 30px;
         padding-left: 20px;
         font-size: @font-size-small;
         color: @color-text-l;
         background: @color-highlight-background;
 				}
       .list-group-item{
         display: flex;
         align-items: center;
         padding: 20px 0 0 30px;
         .avatar{
           width: 50px;
           height: 50px;
           border-radius: 50%;
 					}
         .name{
           margin-left:20px;
           color:@color-text-l;
           font-size:@font-size-medium;
 				  }
					
 				}
 			 }
			 .list-shortcut{
			 	position: absolute;
			 	z-index: 30;
			 	right: 0;
			 	top: 50%;
			 	transform: translateY(-50%);
			 	width: 20px;
			 	padding: 20px 0;
			 	border-radius: 10px;
			 	text-align: center;
			 	background: @color-background-d;
			 	font-family: Helvetica;
			 	.item{
			 		padding: 3px;
			 		line-height: 1;
			 		color: @color-text-l;
			 		font-size: @font-size-small;
			 		&.current{
			 			color: @color-theme;
			 	}
			 }
			 }
			 .list-fixed{
			 	position: absolute;
			 	top: 0;
			 	left: 0;
			 	width: 100%;
			 	.fixed-title{
			 		height: 30px;
			 		line-height: 30px;
			 		padding-left: 20px;
			 		font-size: @font-size-small;
			 		color: @color-text-l;
			 		background: @color-highlight-background;
			 	}
			 }
			 .loading-container{
			 	position: absolute;
			 	width: 100%;
			 	top: 50%;
			 	transform: translateY(-50%);
			 }
	
 		}
</style>

    
   
 	